1. Field of the Invention
The present invention relates to a magnetic resonance imaging apparatus and a magnetic resonance imaging method that collect magnetic resonance signals concerning a subject in a fast spin echo (FSE) sequence or a fast asymmetric spin echo (FASE) sequence.
2. Description of the Related Art
In this type of magnetic resonance imaging, a phase shift of spin echoes is detected based on pre-scan. In main scan, the detected phase shift is corrected.
For example, according to a technology disclosed in U.S. Pat. No. 6,369,568, spin echoes which are not subjected to phase encoding (PE) are collected, and zeroth order and first order phase differences of a first echo and a second echo are measured. Further, the zeroth order phase difference is mainly corrected by adjusting a phase of an RF at the time of main scan, and the first order phase difference is corrected by adding a correction pulse to a gradient magnetic field pulse in a readout direction at the time of main scan.
It is to be noted that a correction amount for a phase shift varies depending on each slice when the main scan is performed with respect to a plurality of slices. Furthermore, when a method of filling a k-space while rotating a blade (see, e.g., Magnetic Resonance in Medicine Vol 42, 963-969, 1999) is applied to the main scan, a correction amount for a phase shift varies depending on each blade.
Therefore, pre-scan is carried out with respect to all slices or blades as targets of the main scan.
As explained above, since the pre-scan is carried out with respect to all slices or blades as targets of the main scan in the conventional technology, a time required for the pre-scan is long depending on imaging conditions.